New formula: makeheaders

A tiny but powerful utility from the sqlite and fossil folks (it's used by both projects) for more scalable C/C++ codebases (read: cheaper to maintain), in the flavor of source-also-declares-interface--style development, vaguely similar to Go (Golang).  `makeheaders` is the **source** preprocessor that generates headers that makes the magic happen.  Also, it can generate the externally-exported library header too (`-H` instead of `-h`)! 

The github packaging makes it available to everyone that likes versioning / automation, i.e., a package manager and/or configuration management.
Reverting back to the regular version:

```shell
0 ~ git:master ❯❯❯ brew info makeheaders                                                ✱
makeheaders: stable 1, HEAD
http://www.hwaci.com/sw/mkhdr/
/usr/local/Cellar/makeheaders/1.4-1 (5 files, 64K) *
  Built from source
From: https://github.com/Homebrew/homebrew/blob/master/Library/Formula/makeheaders.rb
==> Dependencies
Build: automake ✔, autoconf ✔
0 ~ git:master ❯❯❯ brew uninstall makeheaders                                           ✱
Uninstalling /usr/local/Cellar/makeheaders/1.4-1...
1 ~ git:master ❯❯❯ brew install makeheaders                                           ⏎ ✱
==> Downloading https://github.com/steakknife/makeheaders/archive/1.4-1.tar.gz
######################################################################## 100.0%
==> ./bootstrap
==> ./configure --disable-silent-rules --prefix=/usr/local/Cellar/makeheaders/1
==> make install
🍺  /usr/local/Cellar/makeheaders/1: 5 files, 52K, built in 8 seconds
0 ~ git:master ❯❯❯
```